This invention relates generally to the field of graphics controllers and more particularly to the field of graphics controllers for controlling flat-panel type displays.
Portable computers typically include what is called generically a flat panel displays Flat-panel type displays can take a variety of forms, the most common of which is the liquid crystal type display. Liquid crystal displays include active matrix type which are also called TFT (Thin Film Transistor) type and passive matrix type which are also called STN (Super Twisted Nematic) type. Both of these are available in monochromatic or color versions. Such flat panel displays are driven by a controller which is typically a portion of an integrated circuit chip and also is referred to as a display controller or an LCD controller.
Liquid crystal displays have a number of well known characteristics which must be overcome by the associated controller. One characteristic is that if the various display pixels (picture elements) are excited so that adjacent picture elements are excited in the same phase, undesirable visual artifacts appear, degrading the quality of the resulting image. These artifacts include visual flickering, and a streaming motion. Frame Rate Control (FRC), which involves introduction of a phase shift for excitation of adjacent pixels in certain types of LCD controllers, is one technique for reducing certain of the aforementioned characteristics.
STN type displays are typically characterized by a panel response time which indicates the response of the panel to stimulation of the pixels contained therein. Displays with faster response times are generally capable of providing more visually pleasing images and innovations in panel technology are leading to STN panels with response times of approximately 150 milliseconds (ms) and faster to response times of 100 ms. TFT panels are characterized by a faster response time of approximately 60 ms. However, the above described frame rate control technique tends to cause increased flickering in panels with fast response times. In addition, in certain TFT and STN panels, such as those employing pseudo 256 gray-shade display, roughness in the form of dither patterns can appear on the panel. It would therefore be desirable to have a flat-panel display controller which adequately compensates for the aforementioned characteristics to provide visually pleasing images on an associated flat-panel display.
The present invention advantageously provides a display controller that compensates for the physical characteristics of modern flat-panel type displays to provide visually pleasing images which are free of many of the aforementioned undesirable visual artifacts. In a principal aspect, embodiments of the present invention employ a dither controller which provides distributed and/or dynamic dithering to render smooth 256 gray-shade images on an associated flat-panel display. The aforementioned distributed and dynamic dithering is advantageously programmable to allow for customization and fine tuning of the dither controller with different types of flat-panel displays. A significant advantage of such dithering is increased stability and smoothness in gray-scale shading for TFT and STN type panels. Other embodiments perform phase and intensity control of RGB (Red, Green, Blue) components of pixel data to reduce screen flicker and increase stability in gray-scale shading for STN type panels. In other embodiments, the aforementioned phase and intensity control is responsive to data produced by the aforementioned dynamic and distributed dithering mechanisms.
These and other features and advantages of the present invention may be better understood by considering the following detailed description of a preferred embodiment of the invention. In the course of this description, reference will frequently be made to the attached drawings.